This NSA classification guide, dated 21 November 2011, covers signals intelligence material that as to be kept secret for more than the standard 60 years: see the Der Spiegel article The NSA in Germany: Snowden’s Documents Available for Download, 18 June 2014.

This NSA presentation from 2012 discusses techniques for subverting “lawful intercept” systems used abroad: see the Intercept article A Death in Athens: Did a Rogue NSA Operation Cause the Death of a Greek Telecom Employee?, 29 September 2015.

This internal NSA post from September 2006 describes the evolution of the European Security Operations Center and the focus of the US-German collaboration in signals intelligence: see the Der Spiegel article Terrorverdächtige: NSA nutzte Erkenntnisse aus Deutschland-Filiale für Tötungen, 15 June 2014.

﻿(U//FOUOKTh^European. Security Center to Become the 'ESOC'
FROM:
A&P‘s Director, Enterprise Management (S2)
Run Date: 09/11/2006
(S//SI) NSA to help build up capabilities of the intell...

Beginning in 2003, a team of NSA counterterrorism analysts based at NSA/CSS Europe began a dedicated project to support counterterrorism efforts in North Africa. The team collected signals intelligence, which they distributed to U.S. European Command and U.S. ambassadors, who then transmitted this information to governments in Mali, Algeria, and Mauritania. They believe this effort was "responsible for the capture or kill of over 40 terrorists."